Claude review: gpu: nova-core: bitfield: fix broken Default implementation

[Claude Code Review Bot <claude-review@example.com>]

Patch Review

**Bug analysis:** The existing code at line 317-323 of `bitfield.rs` is:

```rust
#[allow(unused_mut)]
let mut value = Self(Default::default());

::kernel::macros::paste!(
$(
value.[<set_ $field>](Default::default());
)*
);
```

The `set_*` methods have the signature `fn [<set_ $field>](mut self, value: $to_type) -> Self` — they take `self` by value, mutate the copy, and return it. Since the struct derives `Copy`, calling `value.set_field(...)` copies `value` into the method, but the returned (modified) copy is discarded. The original `value` retains the zero-initialized storage, so field defaults are silently lost.

**Fix correctness:** The patch changes to:

```rust
let value = Self(Default::default());

::kernel::macros::paste!(
$(
let value = value.[<set_ $field>](Default::default());
)*
);
```

This correctly rebinds `value` to the returned modified copy on each iteration. The removal of `mut` and `#[allow(unused_mut)]` is appropriate since shadowing replaces mutation.

**Test quality:** The kunit test is well-designed — it uses a `State` enum where `#[default]` is `Active = 1` (not the zero value), which means the test would fail without the fix (the u32 storage defaults to 0, which maps to `Inactive`). This is a good discriminating test.

**Minor notes:**

- The `use kernel::prelude::*;` import is added for the `#[kunit_tests]` attribute macro and `Result` type in the test. This is fine.
- The `From<bool>` / `From<State>` trait impls in the test mirror the pattern used in the module's doc examples, which is consistent.

**Nit (non-blocking):** The test only covers the `=> $into_type` path (bool-to-enum conversion). It doesn't test the plain `as $type` or `?=> $try_into_type` paths, but that's acceptable for a bugfix — the core issue (discarded return value) affects all paths equally, and one test is sufficient to demonstrate the fix works.

No issues found. This is a clean, correct bugfix.

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Generated by Claude Code Patch Reviewer